diff --git a/include/guisan/actionevent.hpp b/include/guisan/actionevent.hpp
index c971bca..11aa15c 100644
--- a/include/guisan/actionevent.hpp
+++ b/include/guisan/actionevent.hpp
@@ -98,7 +98,7 @@ namespace gcn
          * @param source The source widget of the event.
          * @param id An identifier of the event.
          */
-        ActionEvent(Widget* source, const std::string& id);
+        ActionEvent(Widget* source, std::string id);
 
         /**
          * Destructor.
diff --git a/include/guisan/exception.hpp b/include/guisan/exception.hpp
index 2365026..7dc9b5b 100644
--- a/include/guisan/exception.hpp
+++ b/include/guisan/exception.hpp
@@ -109,7 +109,7 @@ namespace gcn
          *
          * @param message The error message of the exception.
          */
-        Exception(const std::string& message);
+        Exception(std::string message);
 
         /**
          * Constructor.
@@ -124,9 +124,9 @@ namespace gcn
          * @param line The line number in the source code where the exception
          *             occured.
          */
-        Exception(const std::string& message,
-                  const std::string& function,
-                  const std::string& filename,
+        Exception(std::string message,
+                  std::string function,
+                  std::string filename,
                   unsigned int line);
 
         /**
diff --git a/include/guisan/imagefont.hpp b/include/guisan/imagefont.hpp
index 0dadc3f..5991dc9 100644
--- a/include/guisan/imagefont.hpp
+++ b/include/guisan/imagefont.hpp
@@ -230,7 +230,7 @@ pqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"); @endcode
          *         with the font.
          * @throws Exception when no glyph is found.
          */
-        Rectangle scanForGlyph(unsigned char glyph, int x, int y, const Color& separator);
+        Rectangle scanForGlyph(unsigned char glyph, int x, int y, const Color& separator) const;
 
         /**
          * Holds the glyphs areas in the image.
diff --git a/include/guisan/widgets/button.hpp b/include/guisan/widgets/button.hpp
index 63307c0..cad9fe8 100644
--- a/include/guisan/widgets/button.hpp
+++ b/include/guisan/widgets/button.hpp
@@ -93,7 +93,7 @@ namespace gcn
          *
          * @param caption the caption of the Button.
          */
-        Button(const std::string& caption);
+        Button(std::string caption);
 
         /**
          * Sets the Button caption.
diff --git a/include/guisan/widgets/dropdown.hpp b/include/guisan/widgets/dropdown.hpp
index 58e4574..4f905ad 100644
--- a/include/guisan/widgets/dropdown.hpp
+++ b/include/guisan/widgets/dropdown.hpp
@@ -129,7 +129,7 @@ namespace gcn
          * @param selected the selected item as an index from the list model.
          * @see getSelected
          */
-        void setSelected(int selected);
+        void setSelected(int selected) const;
 
         /**
          * Sets the list model to use when displaying the list.
diff --git a/src/exception.cpp b/src/exception.cpp
index f63d0dd..8d9af3a 100644
--- a/src/exception.cpp
+++ b/src/exception.cpp
@@ -71,22 +71,21 @@ namespace gcn
 
     }
 
-    Exception::Exception(const std::string& message)
+    Exception::Exception(std::string message)
         : mFunction("?"),
-          mMessage(message),
+          mMessage(std::move(message)),
           mFilename("?"),
           mLine(0)
     {
-
     }
 
-    Exception::Exception(const std::string& message,
-                         const std::string& function,
-                         const std::string& filename,
+    Exception::Exception(std::string message,
+                         std::string function,
+                         std::string filename,
                          unsigned int line)
-                         : mFunction(function),
-                           mMessage(message),
-                           mFilename(filename),
+                         : mFunction(std::move(function)),
+                           mMessage(std::move(message)),
+                           mFilename(std::move(filename)),
                            mLine(line)
     {
 
diff --git a/src/focushandler.cpp b/src/focushandler.cpp
index 506bf7c..6eaac93 100644
--- a/src/focushandler.cpp
+++ b/src/focushandler.cpp
@@ -221,13 +221,13 @@ namespace gcn
         {
             mFocusedWidget = mWidgets.at(focusedWidget);
 
-            Event focusEvent(mFocusedWidget);
+            const Event focusEvent(mFocusedWidget);
             distributeFocusGainedEvent(focusEvent);
         }
 
         if (focused >= 0)
         {
-            Event focusEvent(mWidgets.at(focused));
+            const Event focusEvent(mWidgets.at(focused));
             distributeFocusLostEvent(focusEvent);
         }
     }
@@ -249,7 +249,7 @@ namespace gcn
                 focusedWidget = i;
             }
         }
-        int focused = focusedWidget;
+        const int focused = focusedWidget;
 
         // i is a counter that ensures that the following loop
         // won't get stuck in an infinite loop
@@ -281,13 +281,13 @@ namespace gcn
         if (focusedWidget >= 0)
         {
             mFocusedWidget = mWidgets.at(focusedWidget);
-            Event focusEvent(mFocusedWidget);
+            const Event focusEvent(mFocusedWidget);
             distributeFocusGainedEvent(focusEvent);
         }
 
         if (focused >= 0)
         {
-            Event focusEvent(mWidgets.at(focused));
+            const Event focusEvent(mWidgets.at(focused));
             distributeFocusLostEvent(focusEvent);
         }
     }
@@ -388,7 +388,7 @@ namespace gcn
                 focusedWidget = i;
             }
         }
-        int focused = focusedWidget;
+        const int focused = focusedWidget;
         bool done = false;
 
         // i is a counter that ensures that the following loop
@@ -429,13 +429,13 @@ namespace gcn
         if (focusedWidget >= 0)
         {
             mFocusedWidget = mWidgets.at(focusedWidget);
-            Event focusEvent(mFocusedWidget);
+            const Event focusEvent(mFocusedWidget);
             distributeFocusGainedEvent(focusEvent);
         }
 
         if (focused >= 0)
         {
-            Event focusEvent(mWidgets.at(focused));
+            const Event focusEvent(mWidgets.at(focused));
             distributeFocusLostEvent(focusEvent);
         }
     }
@@ -465,7 +465,7 @@ namespace gcn
                 focusedWidget = i;
             }
         }
-        int focused = focusedWidget;
+        const int focused = focusedWidget;
         bool done = false;
 
         // i is a counter that ensures that the following loop
@@ -506,13 +506,13 @@ namespace gcn
         if (focusedWidget >= 0)
         {
             mFocusedWidget = mWidgets.at(focusedWidget);
-            Event focusEvent(mFocusedWidget);
+            const Event focusEvent(mFocusedWidget);
             distributeFocusGainedEvent(focusEvent);
         }
 
         if (focused >= 0)
         {
-            Event focusEvent(mWidgets.at(focused));
+            const Event focusEvent(mWidgets.at(focused));
             distributeFocusLostEvent(focusEvent);
         }
     }
diff --git a/src/genericinput.cpp b/src/genericinput.cpp
index e4722a3..cd67c11 100644
--- a/src/genericinput.cpp
+++ b/src/genericinput.cpp
@@ -138,14 +138,12 @@ namespace gcn
 
     KeyInput GenericInput::dequeueKeyInput()
     {
-        KeyInput keyInput;
-
         if (mKeyInputQueue.empty())
         {
             throw GCN_EXCEPTION("The queue is empty.");
         }
 
-        keyInput = mKeyInputQueue.front();
+        const KeyInputkeyInput = mKeyInputQueue.front();
         mKeyInputQueue.pop();
 
         return keyInput;
@@ -158,14 +156,12 @@ namespace gcn
 
     MouseInput GenericInput::dequeueMouseInput()
     {
-        MouseInput mouseInput;
-        
         if (mMouseInputQueue.empty())
         {
             throw GCN_EXCEPTION("The queue is empty.");
         }
         
-        mouseInput = mMouseInputQueue.front();
+        const MouseInput mouseInput = mMouseInputQueue.front();
         mMouseInputQueue.pop();
         
         return mouseInput;        
diff --git a/src/imagefont.cpp b/src/imagefont.cpp
index 6b6fb81..7b9e0c3 100644
--- a/src/imagefont.cpp
+++ b/src/imagefont.cpp
@@ -170,7 +170,7 @@ namespace gcn
         mFilename = filename;
         mImage = Image::load(filename, false);
 
-        Color separator = mImage->getPixel(0, 0);
+        const Color separator = mImage->getPixel(0, 0);
 
         int i = 0;
         for (i=0; separator == mImage->getPixel(i, 0)
@@ -284,7 +284,7 @@ namespace gcn
         return mGlyphSpacing;
     }
 
-    Rectangle ImageFont::scanForGlyph(unsigned char glyph, int x, int y, const Color& separator)
+    Rectangle ImageFont::scanForGlyph(unsigned char glyph, int x, int y, const Color& separator) const
     {
         Color color;
         do
diff --git a/src/sdl/sdl2graphics.cpp b/src/sdl/sdl2graphics.cpp
index ca9c521..499bddb 100644
--- a/src/sdl/sdl2graphics.cpp
+++ b/src/sdl/sdl2graphics.cpp
@@ -225,10 +225,11 @@ namespace gcn
 
         if (mAlpha)
         {
-            int x1 = area.x > top.x ? area.x : top.x;
-            int y1 = area.y > top.y ? area.y : top.y;
-            int x2 = area.x + area.width < top.x + top.width ? area.x + area.width : top.x + top.width;
-            int y2 = area.y + area.height < top.y + top.height ? area.y + area.height : top.y + top.height;
+            const int x1 = area.x > top.x ? area.x : top.x;
+            const int y1 = area.y > top.y ? area.y : top.y;
+            const int x2 = area.x + area.width < top.x + top.width ? area.x + area.width : top.x + top.width;
+            const int y2 = area.y + area.height < top.y + top.height ? area.y + area.height : top.y + top.height;
+
             SDL_Rect rect;
             rect.x = x1;
             rect.y = y1;
@@ -381,10 +382,10 @@ namespace gcn
         
     void SDL2Graphics::drawRectangle(const Rectangle& rectangle)
     {
-        int x1 = rectangle.x;
-        int x2 = rectangle.x + rectangle.width - 1;
-        int y1 = rectangle.y;
-        int y2 = rectangle.y + rectangle.height - 1;
+        const int x1 = rectangle.x;
+        const int x2 = rectangle.x + rectangle.width - 1;
+        const int y1 = rectangle.y;
+	const int y2 = rectangle.y + rectangle.height - 1;
 
         drawHLine(x1, y1, x2);
         drawHLine(x1, y2, x2);
diff --git a/src/sdl/sdlgraphics.cpp b/src/sdl/sdlgraphics.cpp
index d18406a..630457b 100644
--- a/src/sdl/sdlgraphics.cpp
+++ b/src/sdl/sdlgraphics.cpp
@@ -108,7 +108,7 @@ namespace gcn
     bool SDLGraphics::pushClipArea(Rectangle area)
     {
         SDL_Rect rect;
-        bool result = Graphics::pushClipArea(area);
+        const bool result = Graphics::pushClipArea(area);
 
         const ClipRectangle& carea = mClipStack.top();
         rect.x = carea.x;
@@ -194,11 +194,10 @@ namespace gcn
 
         if (mAlpha)
         {
-            int x1 = area.x > top.x ? area.x : top.x;
-            int y1 = area.y > top.y ? area.y : top.y;
-            int x2 = area.x + area.width < top.x + top.width ? area.x + area.width : top.x + top.width;
-            int y2 = area.y + area.height < top.y + top.height ? area.y + area.height : top.y + top.height;
-            int x, y;
+            const int x1 = area.x > top.x ? area.x : top.x;
+            const int y1 = area.y > top.y ? area.y : top.y;
+            const int x2 = area.x + area.width < top.x + top.width ? area.x + area.width : top.x + top.width;
+            const int y2 = area.y + area.height < top.y + top.height ? area.y + area.height : top.y + top.height;
 
             SDL_LockSurface(mTarget);
             for (y = y1; y < y2; y++)
@@ -219,7 +218,7 @@ namespace gcn
             rect.w = area.width;
             rect.h = area.height;
 
-            Uint32 color = SDL_MapRGBA(mTarget->format, mColor.r, mColor.g, mColor.b, mColor.a);
+            const Uint32 color = SDL_MapRGBA(mTarget->format, mColor.r, mColor.g, mColor.b, mColor.a);
             SDL_FillRect(mTarget, &rect, color);
         }
     }
@@ -289,7 +288,7 @@ namespace gcn
             x2 = top.x + top.width -1;
         }
 
-        int bpp = mTarget->format->BytesPerPixel;
+        const int bpp = mTarget->format->BytesPerPixel;
 
         SDL_LockSurface(mTarget);
 
@@ -400,7 +399,7 @@ namespace gcn
             y2 = top.y + top.height - 1;
         }
 
-        int bpp = mTarget->format->BytesPerPixel;
+        const int bpp = mTarget->format->BytesPerPixel;
 
         SDL_LockSurface(mTarget);
 
@@ -472,10 +471,10 @@ namespace gcn
 
     void SDLGraphics::drawRectangle(const Rectangle& rectangle)
     {
-        int x1 = rectangle.x;
-        int x2 = rectangle.x + rectangle.width - 1;
-        int y1 = rectangle.y;
-        int y2 = rectangle.y + rectangle.height - 1;
+        const int x1 = rectangle.x;
+        const int x2 = rectangle.x + rectangle.width - 1;
+        const int y1 = rectangle.y;
+	const int y2 = rectangle.y + rectangle.height - 1;
 
         drawHLine(x1, y1, x2);
         drawHLine(x1, y2, x2);
@@ -510,8 +509,8 @@ namespace gcn
 
         // Draw a line with Bresenham
 
-        int dx = ABS(x2 - x1);
-        int dy = ABS(y2 - y1);
+        const int dx = ABS(x2 - x1);
+        const int dy = ABS(y2 - y1);
 
         if (dx > dy)
         {
diff --git a/src/widgets/button.cpp b/src/widgets/button.cpp
index 229f216..5e9869b 100644
--- a/src/widgets/button.cpp
+++ b/src/widgets/button.cpp
@@ -85,8 +85,8 @@ namespace gcn
         addFocusListener(this);
     }
 
-    Button::Button(const std::string& caption)
-            : mCaption(caption),
+    Button::Button(std::string caption)
+            : mCaption(std::move(caption)),
               mHasMouse(false),
               mKeyPressed(false),
               mMousePressed(false),
@@ -264,7 +264,7 @@ namespace gcn
 
     void Button::keyPressed(KeyEvent& keyEvent)
     {
-        Key key = keyEvent.getKey();
+        const Key key = keyEvent.getKey();
 
         if (key.getValue() == Key::Enter
             || key.getValue() == Key::Space)
@@ -276,7 +276,7 @@ namespace gcn
 
     void Button::keyReleased(KeyEvent& keyEvent)
     {
-        Key key = keyEvent.getKey();
+        const Key key = keyEvent.getKey();
 
         if ((key.getValue() == Key::Enter
              || key.getValue() == Key::Space)
diff --git a/src/widgets/checkbox.cpp b/src/widgets/checkbox.cpp
index a65a30a..9d9e0cc 100644
--- a/src/widgets/checkbox.cpp
+++ b/src/widgets/checkbox.cpp
@@ -173,7 +173,7 @@ namespace gcn
 
     void CheckBox::keyPressed(KeyEvent& keyEvent)
     {
-        Key key = keyEvent.getKey();
+        const Key key = keyEvent.getKey();
 
         if (key.getValue() == Key::Enter ||
             key.getValue() == Key::Space)
@@ -198,7 +198,7 @@ namespace gcn
 
     void CheckBox::adjustSize()
     {
-        int height = getFont()->getHeight();
+        const int height = getFont()->getHeight() + 2;
 
         setHeight(height);
         setWidth(getFont()->getWidth(mCaption) + height + height / 2);
diff --git a/src/widgets/dropdown.cpp b/src/widgets/dropdown.cpp
index 653e33b..217988f 100644
--- a/src/widgets/dropdown.cpp
+++ b/src/widgets/dropdown.cpp
@@ -219,7 +219,7 @@ namespace gcn
     {
         Color faceColor, highlightColor, shadowColor;
         int offset;
-        int alpha = getBaseColor().a;
+        const int alpha = getBaseColor().a;
 
         if (mPushed)
         {
@@ -276,7 +276,7 @@ namespace gcn
         return mListBox->getSelected();
     }
 
-    void DropDown::setSelected(int selected)
+    void DropDown::setSelected(int selected) const
     {
         if (selected >= 0)
         {
@@ -419,7 +419,7 @@ namespace gcn
 
         if (mDroppedDown && getParent())
         {
-            int h = getParent()->getChildrenArea().height - getY();
+            const int h = getParent()->getChildrenArea().height - getY();
 
             if (listBoxHeight > h - h2 - 2)
             {
diff --git a/src/widgets/imagebutton.cpp b/src/widgets/imagebutton.cpp
index 68d11bd..e01ea10 100644
--- a/src/widgets/imagebutton.cpp
+++ b/src/widgets/imagebutton.cpp
@@ -123,7 +123,7 @@ namespace gcn
     {
         gcn::Color faceColor = getBaseColor();
         gcn::Color highlightColor, shadowColor;
-        int alpha = getBaseColor().a;
+        const int alpha = getBaseColor().a;
 
         if (isPressed())
         {
diff --git a/src/widgets/listbox.cpp b/src/widgets/listbox.cpp
index 8f96759..213d42c 100644
--- a/src/widgets/listbox.cpp
+++ b/src/widgets/listbox.cpp
@@ -216,7 +216,7 @@ namespace gcn
 
     void ListBox::keyPressed(KeyEvent& keyEvent)
     {
-        Key key = keyEvent.getKey();
+        const Key key = keyEvent.getKey();
 
         if (key.getValue() == Key::Enter || key.getValue() == Key::Space)
         {
diff --git a/src/widgets/radiobutton.cpp b/src/widgets/radiobutton.cpp
index 1c87d76..29a5c0c 100644
--- a/src/widgets/radiobutton.cpp
+++ b/src/widgets/radiobutton.cpp
@@ -117,7 +117,7 @@ namespace gcn
             graphics->drawRectangle(Rectangle(0, 0, getWidth(), getHeight()));
         }
 
-        int h = getHeight() + getHeight() / 2;
+        const int h = getHeight() + getHeight() / 2;
 
         graphics->drawText(getCaption(), h - 2, 0);
     }
@@ -135,7 +135,7 @@ namespace gcn
             h = getHeight() - 3;
         }
 
-        int alpha = getBaseColor().a;
+        const int alpha = getBaseColor().a;
         Color faceColor = getBaseColor();
         faceColor.a = alpha;
         Color highlightColor = faceColor + 0x303030;
@@ -149,7 +149,7 @@ namespace gcn
         graphics->setColor(backCol);
 
         int i;
-        int hh = (h + 1) / 2;
+        const int hh = (h + 1) / 2;
 
         for (i = 1; i <= hh; ++i)
         {
@@ -177,7 +177,7 @@ namespace gcn
 
         graphics->setColor(getForegroundColor());
 
-        int hhh = hh - 3;
+        const int hhh = hh - 3;
         if (mSelected)
         {
             for (i = 0; i < hhh; ++i)
@@ -230,7 +230,7 @@ namespace gcn
 
     void RadioButton::keyPressed(KeyEvent& keyEvent)
     {
-        Key key = keyEvent.getKey();
+        const Key key = keyEvent.getKey();
 
         if (key.getValue() == Key::Enter ||
             key.getValue() == Key::Space)
@@ -290,7 +290,7 @@ namespace gcn
 
     void RadioButton::adjustSize()
     {
-        int height = getFont()->getHeight();
+        const int height = getFont()->getHeight();
 
         setHeight(height);
         setWidth(getFont()->getWidth(getCaption()) + height + height / 2);
diff --git a/src/widgets/slider.cpp b/src/widgets/slider.cpp
index 7e9c9c7..9e21b2c 100644
--- a/src/widgets/slider.cpp
+++ b/src/widgets/slider.cpp
@@ -146,9 +146,9 @@ namespace gcn
 
     void Slider::drawMarker(gcn::Graphics* graphics)
     {
-        gcn::Color faceColor = getBaseColor();
+        const gcn::Color faceColor = getBaseColor();
         Color highlightColor, shadowColor;
-        int alpha = getBaseColor().a;
+        const int alpha = getBaseColor().a;
         if (isEnabled())
         {
             highlightColor = faceColor + 0x303030;
@@ -166,7 +166,7 @@ namespace gcn
 
         if (getOrientation() == Horizontal)
         {
-            int v = getMarkerPosition();
+            const int v = getMarkerPosition();
             graphics->fillRectangle(gcn::Rectangle(v + 1, 1, getMarkerLength() - 2, getHeight() - 2));
             graphics->setColor(highlightColor);
             graphics->drawLine(v, 0, v + getMarkerLength() - 1, 0);
@@ -183,7 +183,7 @@ namespace gcn
         }
         else
         {
-            int v = (getHeight() - getMarkerLength()) - getMarkerPosition();
+            const int v = (getHeight() - getMarkerLength()) - getMarkerPosition();
             graphics->fillRectangle(gcn::Rectangle(1, v + 1, getWidth() - 2, getMarkerLength() - 2));
             graphics->setColor(highlightColor);
             graphics->drawLine(0, v, 0, v + getMarkerLength() - 1);
@@ -271,7 +271,7 @@ namespace gcn
 
     void Slider::keyPressed(KeyEvent& keyEvent)
     {
-        Key key = keyEvent.getKey();
+        const Key key = keyEvent.getKey();
 
         if (getOrientation() == Horizontal)
         {
@@ -327,7 +327,7 @@ namespace gcn
             w = getHeight();
         }
 
-        double pos = v / ((double)w - getMarkerLength());
+        const double pos = v / ((double)w - getMarkerLength());
         return (1.0 - pos) * getScaleStart() + pos * getScaleEnd();
     }
 
@@ -343,7 +343,7 @@ namespace gcn
             v = getHeight();
         }
 
-        int w = (int)((v - getMarkerLength())
+        const int w = (int)((v - getMarkerLength())
             * (value - getScaleStart())
             / (getScaleEnd() - getScaleStart()));
 
diff --git a/src/widgets/textbox.cpp b/src/widgets/textbox.cpp
index f6a3b8b..4e8618b 100644
--- a/src/widgets/textbox.cpp
+++ b/src/widgets/textbox.cpp
@@ -145,7 +145,7 @@ namespace gcn
 
     void TextBox::keyPressed(KeyEvent& keyEvent)
     {
-        Key key = keyEvent.getKey();
+        const Key key = keyEvent.getKey();
 
         if (key.getValue() == Key::Left)
         {
diff --git a/src/widgets/togglebutton.cpp b/src/widgets/togglebutton.cpp
index 0f5a737..a9042d4 100644
--- a/src/widgets/togglebutton.cpp
+++ b/src/widgets/togglebutton.cpp
@@ -85,7 +85,7 @@ namespace gcn
     {
         Color faceColor = getBaseColor();
         Color highlightColor, shadowColor;
-        int alpha = getBaseColor().a;
+        const int alpha = getBaseColor().a;
 
         if (isPressed() || isSelected())
         {
@@ -118,7 +118,7 @@ namespace gcn
         graphics->setColor(getForegroundColor());
 
         int textX;
-        int textY = getHeight() / 2 - getFont()->getHeight() / 2;
+        const int textY = getHeight() / 2 - getFont()->getHeight() / 2;
 
         switch (getAlignment())
         {
@@ -183,7 +183,7 @@ namespace gcn
 
     void ToggleButton::keyReleased(KeyEvent& keyEvent)
     {
-        Key key = keyEvent.getKey();
+        const Key key = keyEvent.getKey();
 
         if ((key.getValue() == Key::Enter
              || key.getValue() == Key::Space)